1. Field of the Invention
The present invention relates to a process for improving the purity and/or whiteness degree of a talc power containing impurities such as dolomite, magnesite and chlorite as well as asbestos.
2. Prior Art
Talc is a hydrous magnesium silicate which is present in the form of a natural mineral. This natural mineral contains impurities such as asbestos, dolomite, magnesite, chlorite, and calcium carbonate. Among these impurities, it is particularly necessary to remove asbestos since its carcinogenicity is becoming a serious problem these days.
Talc is widely used for pharmaceuticals, cosmetics, paints, paper making, plastics, etc. Since pharmaceuticals and cosmetics are applied directly to the human body, it is particularly essential that the talc that is used for them is free from asbestos.
Since talc is, in most cases, used in the form of powder, it is considerably difficult and impractical to effectively remove the asbestos which is mixed in the talc powder. Moreover, both talc and asbestos are chemically stable minerals and therefore difficult to separate by using an ordinary acid or alkali treatment, although trace amounts of talc and asbestos can be eluted from talc powder with a mineral acid such as hydrochloric, sulfuric or nitric acid. The Reference, "INTRODUCTION TO THE MEASUREMENT OF WORKING ENVIRONMENTS" (Revised Second Edition), Page 363, published by Korona-sha on June 5, 1981, discloses a method of measuring the quartz content of quartz and other ores using a weighing method which utilizes the difference between the rates of dissolution of the quartz and other ores in heated phosphoric acid. However, there is no disclosure or teaching with respect to improving the purity and whiteness of talc by utilizing the difference between the rates of dissolution of talc and impurities such as asbestos, etc. in heated phosphoric acid.